Hi LoLo,
The easiest way to send a store item to auction, assuming the store item was originally created through Auctiva, would be to locate that store item on your Auctiva Saved Listings page, change the sale type to "auction" and post it as normal. If you did not create the original store item through Auctiva and therefore do not have a saved listing associated with it, it may be easiest to do this directly through eBay.
Any additional questions or concerns? Please contact our customer support team using the appropriate link on our help page:
http://www.auctiva.com/free-auction-software-help/help.aspx-Mike